Cooling apparatus and frost detecting method thereof

ABSTRACT

A cooling apparatus including a frost sensor to sense frost, a multiplexer having a first input terminal, to which the frost sensor is connected, and a second input terminal as a non-connected input terminal, a signal processor to subtract a signal input through the second input terminal from a signal input through the first input terminal, and to output a signal obtained by the subtraction, and a controller to detect an amount of frost sensed by the frost sensor, based on the output signal from the signal processor. It is possible to easily and accurately determine noise contained in a signal received from the frost sensor by determining, as noise, the signal received from the input terminal, to which the frost sensor is not connected, and subtracting the noise from the signal received from each input terminal, to which the frost sensor is connected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2010-8391 filed on Jan. 29, 2010 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference in its entirety.

BACKGROUND

1. Field

Embodiments relate to a cooling apparatus and a frost detecting method thereof, and, more particularly, to a cooling apparatus capable of directly detecting frost formed on an evaporator due to heat exchange and a frost detecting method thereof.

2. Description of the Related Art

A cooling apparatus is adapted to cool a confined space by circulating a refrigerant through a refrigeration cycle. As such a cooling apparatus, there are a refrigerator, a Kimchi refrigerator, an air conditioner, etc.

Here, the refrigeration cycle includes four stages to change the phase of the refrigerant, namely, compression, condensation, expansion, and vaporization stages. To this end, the cooling system should include a compressor, a condenser, an expansion valve, and an evaporator. When a gaseous refrigerant is supplied to the condenser after being compressed in accordance with operation of a compressor, the refrigerant, which is in a compressed state, is cooled as it exchanges heat with air around the condenser. As a result, the refrigerant is condensed into liquid phase. The liquid refrigerant is then injected into the evaporator while flow rate thereof is adjusted by the expansion valve. As a result, the refrigerant is abruptly expanded, so that it is vaporized. As the refrigerant is vaporized, it absorbs heat from air around the evaporator, thereby generating cold air. The cold air is supplied to a confined space such as a storage chamber or a room, thereby cooling the confined space. The refrigerant, which has been changed into the gaseous phase in the evaporator, is again introduced into the compressor, and is then compressed into the liquid phase. Thus, the above stages of the refrigeration cycle are repeated for the refrigerant.

The surface temperature of the evaporator, which functions to cool a confined space by absorbing heat from the confined space through the refrigeration cycle, is relatively lower than the temperature of air present in the confined space. As a result, moisture condensed from the air in the confined space, which is in a moisture-rich state, is attached to the surface of the evaporator, so that frost is formed on the surface of the evaporator. The frost formed on the surface of the evaporator accumulates over time, so that the thickness of the frost is increased. As a result, the heat exchange efficiency of the cold air flowing around the evaporator is degraded, thereby causing degradation in cooling efficiency and excessive power consumption.

In order to solve such problems, in conventional cases, an operating time of the compressor is accumulated, and a defrosting operation is carried out when the accumulated operating time exceeds a predetermined time. In the defrosting operation, a heater arranged around the evaporator operates to remove the frost formed on the evaporator.

However, this method is inefficient to remove the frost formed on the evaporator because the defrosting operation is periodically carried out based on the operating time of the compressor, irrespective of the actual amount of the frost formed on the evaporator. Furthermore, unnecessary power consumption may occur. Also, an increase in temperature may frequently occur due to the defrosting operation.

To this end, there is a conventional frost detecting apparatus developed to directly detect the amount of frost formed on an evaporator and to efficiently carry out a defrosting operation based on the result of the detection. In the conventional frost detecting apparatus, a voltage corresponding to a drive signal from a multiplexer is supplied to a sensing unit. Based on the supplied voltage, the sensing unit senses a capacitance established at the evaporator and transmits a signal representing the sensed capacitance to a detecting unit. Based on the sensed capacitance, the detecting unit determines the amount of frost formed on the evaporator.

In such a frost detecting apparatus, noise may be generated due to variation in heat generated in various elements such as a multiplexer and a detector. Noise may also be generated due to a frequency generated from an oscillator. The generated noise may be transmitted to the detector in a state of being included in the sensing signal representing the capacitance established at the evaporator. As a result, it may be difficult to accurately determine the amount of frost. For this reason, it may be difficult to carry out a defrosting operation at an appropriate point in time.

SUMMARY

It is an aspect to provide a cooling apparatus capable of easily removing noise from a frost detecting signal generated upon detecting frost formed on an evaporator, and accurately detecting the amount of frost formed, and a frost detecting method thereof.

It is another aspect to provide a cooling apparatus capable of detecting an accurate amount of frost formed in the cooling apparatus, thereby achieving an efficient defrosting operation and a reduction in power consumption, and a frost detecting method thereof.

In accordance with one aspect, a cooling apparatus includes a frost sensor to sense frost, a multiplexer having a first input terminal, to which the frost sensor is connected, and a second input terminal as a non-connected input terminal, a signal processor to subtract a signal input through the second input terminal from a signal input through the first input terminal, and to output a signal obtained by the subtraction, and a controller to detect an amount of frost sensed by the frost sensor, based on the output signal from the signal processor.

A peripheral noise signal may be input to the second input terminal.

The signal processor may remove a noise signal by subtracting the signal input through the second input terminal from a frost sensing signal as the signal input through the first input terminal.

The controller may control a defrosting operation based on the detected frost amount. The cooling apparatus may further include a heater to operate in accordance with a command from the controller, so as to execute the defrosting operation.

The cooling apparatus may further include a filter to allow a low-frequency signal component of a frost sensing signal generated by the frost sensor to pass through the filter.

The signal processor may allow a low-frequency signal component of a frost sensing signal generated by the frost sensor to pass through the signal processor.

The signal processor may convert an analog signal as a frost sensing signal generated by the frost sensor into a digital signal.

The signal processor may amplify a frost sensing signal generated by the frost sensor to a predetermined level.

The frost sensor may be installed on at least one of an evaporator for a refrigerating compartment, an evaporator for a freezing compartment, and an evaporator for an ice making compartment.

The frost sensor may sense a capacitance established between cooling fins provided at the at least one evaporator.

The cooling apparatus may further include an oscillator to supply a voltage to the frost sensor.

The multiplexer may further have a first output terminal, to which the frost sensor is connected, and a second output terminal as a non-connected output terminal, and may supply the voltage to a selected one of the first and second output terminals.

The frost sensor may include a plurality of sensors. The sensors may be connected to the first output terminal and first input terminal of the multiplexer. The sensors may sequentially receive a voltage, and transmit a frost sensing signal to the first input terminal.

A frost detecting method in a cooling apparatus includes supplying a voltage to a frost sensor through a first output terminal of a multiplexer, sensing frost by the frost sensor, receiving a frost sensing signal generated by the frost sensor through a first input terminal of the multiplexer, receiving a signal from a second input terminal of the multiplexer, subtracting the signal of the second input terminal from the frost sensing signal, and detecting an amount of frost, based on a signal obtained by the subtraction.

The subtraction of the signal of the second input terminal from the frost sensing signal may be executed to remove a peripheral noise signal from the frost sensing signal.

The frost detecting method may further include determining a point in time when a defrosting operation should be begun, based on the detected frost amount, driving a heater at the determined time point when the defrosting operation should be begun, determining, during the defrosting operation, a point in time when the defrosting operation should be ended, and stopping driving of the heater at the determined time point when the defrosting operation should be ended.

The frost detecting method may further include passing a low-frequency component of the frost sensing signal generated by the frost sensor.

The frost detecting method may further include converting an analog signal as the frost sensing signal generated by the frost sensor into a digital signal.

The frost detecting method may further include amplifying the frost sensing signal generated by the frost sensor to a predetermined level.

The sensing of frost by the frost sensor may include sensing a capacitance established between cooling fins provided on at least one evaporator.

The frost detecting method may further include supplying a voltage through the second output terminal of the multiplexer.

The second output terminal and the second input terminal may be non-connected terminals.

The frost sensor may include a plurality of sensors each connected to the first output terminal and first input terminal of the multiplexer. The supply of the voltage to the frost sensor may include sequentially supplying the voltage to the sensors.

The reception of the frost sensing signal through the first input terminal of the multiplexer may include sequentially receiving frost sensing signals from the sensors through the first input terminal.

In accordance with one aspect, it may be possible to easily and accurately determine noise contained in a signal received from the frost sensor by determining, as noise, the signal received from the input terminal, to which the frost sensor is not connected, and subtracting the noise from the signal received from each input terminal, to which the frost sensor is connected.

As a result, it may be possible to accurately determine whether or not frost has been formed on an evaporator, and to accurately detect the amount of frost formed.

It may also be possible to execute a defrosting operation at an appropriate point in time as the accuracy of the detection of the amount of frost formed on the evaporator is enhanced. Accordingly, it may be possible to prevent the cooling efficiency of the evaporator from being reduced due to a reduction in air flow rate during heat exchange.

It may be possible to accurately determine the amount of frost left on the evaporator during the defrosting operation, and thus to accurate determine an appropriate point in time when the defrosting operation should be ended. Accordingly, it may be possible to end the defrosting operation at an appropriate point in time. As a result, it may be possible to reduce energy consumption caused by the defrosting operation. Also, the temperature variation in the cooling apparatus may be minimized in accordance with the defrosting operation. Accordingly, the performance of the cooling apparatus may be enhanced.

As the defrosting operation may be efficiently begun and ended, the heater may be driven only when the driving of the heater is required. Accordingly, the driving time of the heater and the number of times the heater drives may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a view illustrating a refrigerator according to an exemplary embodiment;

FIG. 2 is a view illustrating a detailed configuration of an evaporator provided at the refrigerator according to the illustrated embodiment;

FIG. 3 is a block diagram illustrating a control configuration of the refrigerator according to an exemplary embodiment;

FIGS. 4A and 4B are sectional views respectively illustrating frost detecting devices according to exemplary embodiments;

FIG. 5 is a block diagram illustrating a control configuration of the refrigerator according to an exemplary embodiment;

FIG. 6 is a block diagram illustrating a connection between a frost sensor and a detector in a frost detecting device provided at the refrigerator in accordance with an exemplary embodiment;

FIGS. 7 and 8 are schematic views respectively illustrating connections between the evaporator and frost detecting device provided at the refrigerator in accordance with embodiments;

FIG. 9 is a flow chart illustrating frost detection carried out in the refrigerator in accordance with an exemplary embodiment; and

FIGS. 10A-10C depicts graphs of frost sensing signals generated in a refrigerator in accordance with an exemplary embodiment.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments will be described in order to explain the present invention by referring to the figures.

Exemplary embodiments are adapted to enhance the defrosting efficiency of a cooling apparatus and thus to reduce power consumption by accurately detecting whether or not frost has been formed on an evaporator of the cooling apparatus and the amount of frost formed, and controlling driving of a heater based on the results of the detection, thereby controlling a defrosting operation.

The exemplary embodiments are described in conjunction with an example in which the cooling apparatus is applied to a refrigerator.

FIG. 1 is a view illustrating a refrigerator according to an exemplary embodiment. FIG. 2 is a view illustrating a detailed configuration of an evaporator provided at the refrigerator according to the illustrated embodiment. FIG. 3 is a block diagram illustrating a control configuration of the refrigerator according to an exemplary embodiment.

A refrigerator is adapted to store food in a fresh state for a prolonged period of time by maintaining a storage chamber in a low-temperature state through repetition of a refrigeration cycle to sequentially compress, condense, expand, and vaporize a refrigerant.

As shown in FIG. 1, such a refrigerator, which is designated by reference numeral 100, includes a body 110 having an open front side, and a storage chamber 120 defined in the body 110, to store food. The storage chamber 120 is laterally divided into a refrigerating compartment 121 and a freezing compartment 122 by an intermediate barrier wall.

Each of the refrigerating compartment 121 and freezing compartment 122 is open at a front side thereof. Doors 131 and 132 are provided at respective open front sides of the refrigerating and freezing compartments 121 and 122, to shield the compartments 121 and 122 from the outside of the compartments 121 and 122.

A duct (not shown), through which air flows, is formed between the body 110 and one wall of the storage chamber 120. A plurality of holes are formed through the wall of the storage chamber 120. Through the holes, air flows between the storage chamber 120 and the duct.

Installed in the duct are evaporators 141 and 142 to cool ambient air present around the evaporators 141 and 142 in accordance with a cooling operation of absorbing latent heat from the ambient air while evaporating a refrigerant supplied from a condenser (not shown), a fan 150 to suck air from the storage chamber 120 while supplying air passing around the evaporators 141 and 142 to the storage chamber 120, and a heater 160 to remove frost formed on the evaporators 141 and 142.

The refrigerator shown in FIG. 1 includes the evaporator 141, which is installed for the refrigerating compartment 121, and the evaporator 142, which is installed for the freezing compartment 122. Using the refrigerating compartment evaporator 141 and freezing compartment evaporator 142, it may be possible to cool the refrigerating compartment 121 and freezing compartment 122, respectively. Alternatively, it may be possible to cool the refrigerating compartment 121 and freezing compartment 122, using a single evaporator.

Of course, an evaporator for an ice making compartment (not shown) may also be installed in the ice making compartment, to achieve ice making in the ice making compartment.

A compressor 170 to compress and then supply the refrigerant is installed in a machinery chamber defined in a lower portion of the body 110. The condenser (not shown) is also installed in the machinery chamber, to discharge heat from the refrigerant, which has been compressed into a high-temperature and high-pressure state, thereby condensing the refrigerant.

As shown in FIG. 2, the evaporator 141 includes a refrigerant tube 141 a, through which the refrigerant flows, and a plurality of cooling fins 141 b (141 b ₁ and 141 b ₂) mounted to the refrigerant tube 141, to achieve an enhancement in heat exchange efficiency. The evaporator 142 also has the same configuration as the evaporator 141. Accordingly, the following description will be given mainly in conjunction with the evaporator 141.

The evaporators 141 and 142 function to heat-exchange the refrigerant, which is maintained in a low-temperature and low-pressure state, with air present in the storage chamber at a higher temperature than the refrigerant, and thus to evaporate the refrigerant under low-pressure and low-temperature conditions, thereby lowering the internal temperature of the storage chamber.

Since the surface temperatures of the evaporators 141 and 142 are lower than the temperature of the air in the storage chamber, moisture condensed from the air in the storage chamber is attached to the surfaces of the evaporators 141 and 142, thereby forming frost.

In order to remove the frost formed on the evaporators 141 and 142, a defrosting operation is carried out. To control the defrosting operation, driving of the heater 160 is controlled under control of the controller 180.

In order to control the defrosting operation, it is necessary to know whether or not frost has been formed on the evaporator 141 and the amount of frost formed.

To this end, the refrigerator, which is an example of the cooling apparatus, includes a frost detecting device 200 to detect the amount of frost formed on the evaporator 141.

As shown in FIG. 2, the frost detecting device 200 includes a frost sensor 210 installed at at least one of the refrigerant tubes 141 a and plural cooling fins 141 b of the evaporator 141, to sense a capacitance established at the evaporator 141, and a detector 220 to determine the amount of frost corresponding to the capacitance sensed by the frost sensor 210.

In this case, the frost sensor 210 includes two electrodes and two insulators, as shown in FIGS. 4A and 4B.

In detail, as shown in FIG. 4A, the frost sensor 210 includes a first electrode 210 a to sense frost formed between the first electrode 210 a and the second cooling fin 141 b ₂ of the evaporator 141, a first insulator 210 b arranged in contact with the first electrode 210 a, a second electrode 210 c arranged in contact with the first insulator 210 b, and a second insulator 210 d installed on the first cooling fin 141 b ₁ arranged opposite to the second cooling fin 141 b ₂ such that the second insulator 210 d is in contact with the second electrode 210 c.

The first insulator 210 b insulates the first electrode 210 a from the second electrode 210 c. The second insulator 210 d insulates the first cooling fin 141 b 1 arranged opposite to the second cooling fin 141 b 2 from the second electrode 210 c.

The first electrode 210 a is connected to a sensor terminal A. The second electrode 210 c is connected to a shield terminal B. Voltages of equal phase and magnitude are applied to the first and second electrodes 210 a and 210 c via the sensor terminal A and shield terminal B, respectively. Accordingly, it may be possible to prevent an electric field from being established at the side of the first cooling fin 141 b ₁.

An electric field may also be generated between the first electrode 210 a and the second cooling fin 141 b ₂. When frost is formed between the first electrode 210 a and the second cooling fin 141 b ₂, the electric field generated between the first electrode 210 a and the second cooling fin 141 b ₂ may be varied, thereby causing a variation in dielectric field between the first electrode 210 a and the second cooling fin 141 b ₂. As a result, a variation in capacitance occurs. The varied capacitance is output in the form of a voltage signal.

Based on the output voltage, it may be possible to determine whether or not frost has been formed, and the amount of frost formed.

As shown in FIG. 4B, the frost sensor 210 is installed on the first cooling fin 141 b ₁, to sense frost formed between the first cooling fin 141 b ₁ and the second cooling fin 141 b ₂.

The frost sensor 210 includes a first electrode 210 a to sense formation of frost, a first insulator 210 b arranged in contact with the first electrode 210 a, a second electrode 210 c arranged in contact with the first insulator 210 b, and a second insulator 210 d arranged in contact with the second electrode 210 c.

In detail, the second electrode 210 c is arranged in contact with the back surface of the first insulator 210 b. The second electrode 210 c extends around an exposed portion of the first insulator 210 b, so as to surround the exposed portion of the first insulator 210 b.

Thus, the second electrode 210 c extends along the surfaces of the first electrode 210 a, except for the front surface of the first electrode 210 a, so as to surround the side surfaces of the first electrode 210 a. In accordance with this arrangement, the second electrode 210 c functions as a shield to cut off an electric field leaking from side surface edges of the first insulator 210 b and first electrode 210 a.

An insulation gap g is formed between the second electrode 210 b and the first electrode 210 a, to insulate the second electrode 210 c from the first electrode 210 a.

The first electrode 210 a is connected to a sensor terminal A, whereas the second electrode 210 c is connected to a shield terminal B. Voltages of equal phase and magnitude are applied to the first electrode 210 a and second electrode 210 c, respectively. As a result, it may be possible to prevent an electric field from being established at the side of the first cooling fin 141 b ₁.

The frost sensor 210 may prevent the electric field generated from the first electrode 210 from leaking from the side surface edges of the first insulating layer 210 b into a frost sensing region. Thus, it may be possible to prevent the electric field of the first electrode 210 a, which defines a frost detection region, from being varied.

Also, the second electrode 230 may prevent the electric field from leaking from the side surface edges of the first insulator 210 b even when the dielectric constant of the first insulator 210 b varies in accordance with a variation in temperature, thus preventing electric field variation.

That is, the electric field of the first electrode 210 a in the frost sensor 210 is guided only to the second cooling fin 141 b ₂ by the second electrode 210 c. Accordingly, the electric field of the first electrode 210 a may be varied only by frost formed between the first electrode 210 a and the second cooling fin 141 b ₂.

FIG. 3 is a block diagram illustrating a control configuration of the refrigerator according to an exemplary embodiment of the present invention. The refrigerator includes the fan 150, heater 160, compressor 170, controller 180, and frost detecting device 200.

The fan 150 rotates in accordance with a command from the controller 180 in a cooling mode, to suck air from the storage chamber 120, and to supply air passing around the evaporators 141 and 142 to the storage chamber 120.

The heater 160 generates heat in accordance with a command from the controller 180 in a defrosting mode, to remove frost formed on the evaporators 141 and 142.

The compressor 170 compresses a refrigerant in accordance with a command from the controller 180 in a cooling mode, to supply the compressed refrigerant to a condenser (not shown). As the compressed refrigerant is supplied, a cooling cycle operates to cool the storage chamber.

When a voltage output from the detector 220 is lower than a first reference voltage, the controller 180 determines that a defrosting operation should be begun. In this case, the controller 180 performs a control to stop driving of the fan 150 and compressor 170, and to drive the heater 160. Thus, a defrosting operation is carried out.

On the other hand, when the voltage output from the detector 220 during the defrosting operation is higher than a second reference voltage, the controller 180 determines that the defrosting operation should be completed. In this case, the controller 180 performs a control to stop driving of the heater 160, and to drive the fan 150 and compressor 170. Thus, a cooling operation is again carried out.

In this case, the controller 180 drives the compressor 170 in a cooling cycle corresponding to an operation mode set by the user while controlling rotation of the fan 150, to keep the storage chamber at a predetermined temperature.

Amounts of frost respectively corresponding to various voltage values may be experimentally acquired. Based on the acquired frost amounts, a first reference voltage corresponding to a point in time when a defrosting operation should be begun and a second reference voltage corresponding to a point in time when the defrosting operation should be ended may be determined. The determined first and second reference voltages may be previously stored in a memory (not shown).

Alternatively, an initial voltage generated between the frost sensor 210 and the cooling fin 141 b of the evaporator 141 may be experimentally acquired under the condition that the frost sensor 210 is installed at the cooling fin 141 b. In this case, a saturation voltage corresponding to a frost saturation state may also be experimentally acquired. The initial voltage and saturation voltage may be compared with each other, to obtain a comparison voltage. The comparison voltage may be set to the first reference voltage, and the initial voltage may be set to the second reference voltage. The first and second reference voltages may be previously stored in the memory (not shown).

The reason why the second reference voltage is set to the initial voltage is that, when the frost formed on the evaporator 141 is completely removed, the initial voltage is output because there is no frost present between the frost detecting device 200.

The distance between the second cooling fin 141 b ₂, formation of frost upon which is determined, and the frost sensor 210 is varied in accordance with the distance between the first cooling fin 141 b ₁, at which the frost sensor 210 is installed, and the second cooling fin 141 b ₂. As a result, the capacitance C established between the second cooling fin 141 b 2 and the frost sensor 210 is varied (C=kε₀A/d, A: the area of the first electrode, d: the distance between the cooling fins, k: the dielectric constant established between the electrodes, and ε₀: the dielectric constant of a free space.) Since a variation in voltage occurs as the capacitance varies, it may be necessary to take into consideration the distance between the cooling fins when the first and second reference voltages are set.

It may be possible to optimize the defrosting operation by starting the defrosting operation at an appropriate point in time, and completing the defrosting operation at an appropriate point in time. Thus, consumption of electric power may be minimized.

The frost detecting device 200 is installed at each of the evaporators 141 and 142, to detect the amount of frost formed on the associated evaporator 141 or 142. The frost detecting device 200 transmits data representing the detected frost amount to the controller 180.

The frost detecting device 200 includes the frost sensor 210 and detector 220. The configuration of the frost detecting device 200 will be described with reference to FIGS. 5 to 8.

FIG. 5 is a block diagram illustrating a detailed configuration of the frost detecting device 200 provided at the refrigerator in accordance with an exemplary embodiment. FIG. 6 is a block diagram illustrating a connection between the frost sensor 210 and detector 220 in the frost detecting device 200 provided at the refrigerator in accordance with an exemplary embodiment. FIGS. 7 and 8 are schematic views respectively illustrating connections between the evaporator and frost detecting device provided at the refrigerator in accordance with embodiments.

As shown in FIG. 5, the frost detecting device 200 includes the frost sensor 210 and detector 220.

The frost sensor 210 includes a plurality of sensors S(1), S(2), . . . , and S(n−1). The sensors S(1), S(2), . . . , and S(n−1) are installed at selected ones of the cooling fins 141 b of the evaporator.

Each of the sensors S(1), S(2), . . . , and S(n−1) of the frost sensor 210 senses frost formed between the cooling fin, at which the sensor is installed, and the cooling fin facing the sensor-installed cooling fin.

Here, sensing frost means sensing a capacitance established between the sensor-installed cooling fin and the cooling fin facing the sensor-installed cooling fin.

As shown in FIG. 6, the sensors of the frost sensor 210, namely, the first sensor S(1), second sensor S(2), . . . , and n−1-th sensor S(n−1), are connected to a plurality of first output terminals of an output stage 221 a in a multiplexer 221, namely, an A₁ output terminal a(1), an A₂ output terminal a(2), . . . , and an A_(n-1), output terminal a(n−1), respectively, while being connected to a plurality of first input terminals of an input stage 221 b in the multiplexer 221, namely, a B₁ input terminal b(1), a B₂ input terminal b(2), . . . , and a B_(n-1) input terminal b(n−1), respectively.

A voltage is sequentially supplied to the first sensor S(1), second sensor S(2), . . . , and n−1-th sensor S(n−1) of the frost sensor 210 via the output stage 221 a of the multiplexer 221. Each sensor, to which the voltage is supplied, senses a capacitance between the associated facing cooling fins, and transmits a signal representing the sensed capacitance to the input stage 221 b of the multiplexer 221.

The sensors S(1), S(2), . . . , and S(n−1) of the frost sensor 210 may be installed on at least one of the refrigerating compartment evaporator 141, freezing compartment evaporator 142, and ice making compartment evaporator (not shown). This will be described with reference to FIGS. 7 and 8.

FIG. 7 is a schematic view illustrating the case in which a plurality of sensors are installed at one evaporator. The sensors S(1), S(2), . . . , and S(n−1) are installed at different cooling fins of the refrigerating compartment evaporator 141, respectively. Each sensor senses frost formed between the cooling fin, at which the sensor is installed, and the cooling fin facing the sensor-installed cooling fin, and transmits a frost sensing signal to the input stage 221 b of the multiplexer 221.

Of course, a single sensor may be installed at one cooling fin of one evaporator.

FIG. 8 is a schematic view illustrating the case in which a plurality of sensors are installed at a plurality of evaporators. The sensors S(1), S(2), . . . , and S(n−1) are installed at different cooling fins of the refrigerating compartment evaporator 141, and freezing compartment evaporator 142, respectively.

Referring to FIG. 8, it can be seen that the first and second sensors S(1) and S(2) are installed at different cooling fins of the refrigerating compartment evaporator 141, respectively, whereas the n−1-th sensor S(n−1) is installed at one cooling fin of the freezing compartment evaporator 142.

Each of the sensors S(1), S(2), . . . , and S(n−1) senses frost formed between the cooling fin, at which the sensor is installed, and the cooling fin facing the sensor-installed cooling fin, and transmits a frost sensing signal to the input stage 221 b of the multiplexer 221.

That is, each of the sensors S(1), S(2), . . . , and S(n−1) transmit a frost sensing signal to an associated one of the input terminals b(1), B(2), . . . , and b(n−1) provided at the input stage 121 b of the multiplexer 121.

The detector 220 removes a noise signal from the frost sensing signal received from the frost sensor 210, to more accurately detect the frost sensing signal. The detector 220 then transmits the detected frost sensing signal (namely, a voltage signal corresponding to a sensed capacitance) to the controller 180.

As the detector 220 removes the noise signal, it may be possible to obtain only a voltage signal corresponding to the capacitance varied due to the frost formed on the cooling fin of the evaporator.

The detector 220 includes, in addition to the multiplexer 221, an oscillator 222, a filter 223, and a signal processor 224.

The multiplexer 221 includes the output stage 221 a, which outputs a voltage generated from the oscillator 222, and an input stage 221 b, which receives a frost sensing signal generated from the frost sensor 210. This will be described with reference to FIG. 6.

The output stage 221 a includes a plurality of first output terminals a(1), a(2), . . . , and a(n−1), and a single second output terminal a(n).

The first output terminals a(1), a(2), . . . , and a(n−1) are connected to the sensors S(1), S(2), . . . , and S(n−1), respectively, whereas the single second output terminal a(n) is a non-connected (NC) terminal which is not connected to any sensor.

The output stage 221 a receives an output terminal select signal from the signal processor 224.

That is, upon connection of the first output terminals a(1), a(2), . . . , and a(n−1) to the sensors S(1), S(2), . . . , and S(n−1) of the frost sensor 210, respectively, the output stage 221 a selects one first output terminal, which corresponds to a command from the signal processor 224. The output stage 221 a then connects the selected first output terminal to the sensor corresponding to the first output terminal.

When the output stage 221 a receives an AC signal having a reference frequency from the oscillator 222, it outputs the received reference-frequency AC signal to the first output terminals a(1), a(2), . . . , and a(n−1) and the second output terminal a(n).

The output stage 221 a selects one sensor corresponding to an output terminal select signal, to connect the selected sensor thereto, and outputs a voltage generated from the oscillator 222 to the connected sensor.

The output stage 221 a also outputs the voltage generated from the oscillator 222 to the second output terminal a(n), which is not connected to any sensor.

That is, the voltage from the oscillator 222 is output to the second output terminal a(n) when signal sensing is achieved at the second input terminal b(n) corresponding to the second output terminal a(n), in order to cause the noise signal generated due to an oscillation operation of the oscillator 222 and effected on the first input terminals b(1), b(2), . . . , and b(n−1) to be effected on the second input terminal b(n) in the same manner.

The input stage 221 b includes a plurality of first input terminals b(1), b(2), . . . , and b(n−1), and a single second input terminal b(n).

The first input terminals b(1), b(2), . . . , and b(n−1) are connected to the sensors S(1), S(2), . . . , and S(n−1), respectively, whereas the single second input terminal b(n) is a non-connected (NC) terminal which is not connected to any sensor.

The input stage 221 b receives an input terminal select signal from the signal processor 224.

That is, upon connecting the first input terminals b(1), b(2), . . . , and b(n−1) to the sensors S(1), S(2), . . . , and S(n−1), respectively, the input stage 221 b selects one first input terminal, which corresponds to a command from the signal processor 224. The input stage 221 b then connects the selected first input terminal to the sensor corresponding to the first input terminal.

The input stage 221 b connects one of the first input terminals b(1), b(2), . . . , and b(n−1) to a sensor corresponding to the sensor in accordance with a command from the signal processor 224. When the input stage 221 b receives a frost sensing signal from the connected sensor, it transmits the received frost sensing signal to the filter 223.

The input stage 221 b transmits a signal generated from the second input terminal b(n), to which any sensor is not connected, to the filter 223.

The signal received from the second input terminal b(n) includes noise signals generated from the oscillator 222 and multiplexer 221.

The multiplexer 221 sequentially connects the sensors to the oscillator 222 in the order determined in accordance with a command from the signal processor 222, to sequentially supply a voltage to the sensors, and thus to sequentially drive the sensors. Accordingly, formation of frost is sensed through the sensors in a sequential manner. A frost sensing signal generated by each sensor is transmitted to the filter 223.

As shown in FIGS. 7 and 8, the input stage 221 a of the multiplexer 221 transmits the frost sensing signals received from the sensors S(1), S(2), . . . , and S(n−1) to the filter 223, while transmitting a signal from the second input terminal b(n) to the filter 223.

The oscillator 222 generates an AC signal having a reference frequency, and supplies the AC signal to the sensors of the frost sensor 210.

The oscillator 222 supplies voltages to the sensor terminal A and shield terminal B of the frost sensor 210 via the multiplexer 221. In this case, the voltages supplied to the sensor terminal A and shield terminal B have the same phase and magnitude.

The filter 223 filters the frost sensing signal received through each input terminal of the input stage 221 b of the multiplexer 221, and transmits the filtered frost sensing signal to the signal processor 224.

That is, the filter 223 receives the frost sensing signal, which has a reference signal component, from the multiplexer 221, and then removes the reference signal component.

The filter 223 allows only the frequency components of the frost sensing signal, which have a frequency not higher than a predetermined frequency, to pass therethrough, while preventing the remaining frequency components of the frost sensing signal from passing therethrough. For the filter 223, a low-pass filter (LPF) may be used.

Here, the predetermined frequency is a frequency lower than the reference frequency generated from the oscillator 222.

The reason why the frost sensing signal is filtered to have a frequency lower than the reference frequency of the oscillator 222 will be described hereinafter. The dielectric constant established between the sensor and the cooling fin is varied in accordance with the amount of frost formed between the sensor and the cooling fin. In accordance with the variation in dielectric constant, a variation in capacitance occurs, thereby causing a variation in the impedance of the sensor terminal of the sensor. The impedance variation causes the voltage of the sensor terminal to be lower than the voltage of the reference signal in accordance with a voltage division rule. As a result, the frequency of the frost sensing signal is lower than the reference frequency. That is, the reference voltage is removed, in order to obtain a pure frost sensing signal.

The signal processor 224 converts the filtered frost sensing signal into a digital signal. The signal processor 224 then subtracts a non-sensing signal from the frost sensing signal, which has been converted into a digital signal, thereby obtaining a noise-removed frost sensing signal. Thereafter, the signal processor 224 transmits the obtained signal to the controller 180. Here, the filtered frost sensing signal is an analog signal.

That is, the signal processor 224 subtracts the signal input to one of the input terminals b(1), b(2), . . . b(n−1), and b(n), which is not connected to any of the sensors S(1), S(2), . . . , S(n−1), and S(n), namely, the input terminal b(n), from each of the frost sensing signals input to the remaining input terminals, thereby removing offset noise generated from the oscillator 222 and multiplexer 221.

Since the filtered frost sensing signal has a very small level, it may be difficult to discriminate the frost sensing signal. Accordingly, the signal processor 224 may convert the filtered frost sensing signal into a digital signal after amplifying the frost sensing signal to a predetermined level.

The signal processor 224 then performs offset adjustment upon the filtered frost sensing signal.

The signal processor 224 transmits, to the multiplexer 221, a select signal to select one of the plural sensors, when frost sensing is to be performed. In accordance with the select signal, one output terminal and one input terminal of the output and input stages 221 a and 221 b in the multiplexer 221 are connected to the selected sensor.

Software for a low-pass filter function may be loaded in the signal processor 224, in order to allow the signal processor 224 to pass only the frequency components of the frost sensing signal, which have a frequency not higher than a predetermined frequency, while blocking the remaining frequency components. In this case, the filter 223 may be dispensed with.

When the signal processor 224 receives a frost sensing signal from the input stage 221 b of the multiplexer 221, it executes the software, thereby passing only the frequency components of the frost sensing signal, which have a frequency not higher than the predetermined frequency. Accordingly, the signal processor 224 converts the resultant frost sensing signal, which only has desired frequency components, into a digital signal.

FIG. 9 is a flow chart illustrating frost detection carried out in the refrigerator in accordance with an exemplary embodiment.

The signal processor 224 selects one of the plural sensors in accordance with a predetermined order (301), and transmits a signal representing sensing of the sensor, namely, a sensor select signal, to the multiplexer 221.

The multiplexer 221 selects the first output terminal corresponding to the sensor select signal from the signal processor 224, thereby causing the selected sensor to be connected to the oscillator 222. The multiplexer 221 then supplies a voltage to the selected sensor (302).

Thereafter, the multiplexer 221 selects the first input terminal corresponding to the sensor select signal from the signal processor 224, thereby causing the selected sensor to be connected to the filter 223. Subsequently, the multiplexer 221 receives a frost sensing signal (303), and then transmits the received frost sensing signal to the filter 223.

Thereafter, the filter 223 filters the frost sensing signal received from the input terminal of the input stage 221 b of the multiplexer 221, and transmits the filtered frost sensing signal to the signal processor 224.

That is, the filter 223, which is a low pass filter (LPF), receives a frost sensing signal containing a reference frequency component from the multiplexer 221, and removes the reference frequency component from the received frost sensing signal.

The reason why the frost sensing signal is filtered to have a frequency lower than the reference frequency of the oscillator 222 will be described hereinafter. The dielectric constant established between the sensor of the frost sensor and the cooling fin is varied in accordance with the amount of frost formed between the sensor and the cooling fin. In accordance with the variation in dielectric constant, a variation in capacitance occurs, thereby causing a variation in the impedance of the sensor terminal of the sensor. The impedance variation causes the voltage of the sensor terminal to be lower than the voltage of the reference signal in accordance with a voltage division rule. As a result, the frequency of the frost sensing signal is lower than the reference frequency. That is, the reference voltage is removed, in order to obtain a pure frost sensing signal.

It may be possible to allow the signal processor 224 to pass only the frequency components of the frost sensing signal, which have a frequency not higher than a predetermined frequency, while preventing the remaining frequency components, using software loaded in the signal processor 224, for a low-pass filter function. In this case, the filter 223 may be dispensed with.

Since the filtered frost sensing signal has a very small level, it may be difficult to discriminate the frost sensing signal. Accordingly, the signal processor 224 may convert the filtered frost sensing signal into a digital signal after amplifying the frost sensing signal to a predetermined level. Here, the filtered frost sensing signal is an analog signal.

It is then determined whether the frost sensing operation has been completed for all sensors (304). When it is not determined that the frost sensing operation has been completed for all sensors, the signal processor 224 selects a next one of the plural sensors, and transmits a signal representing sensing of the sensor, namely, a sensor select signal, to the multiplexer 221.

In this case, the sensor select signal has been predetermined. If the frost sensing operation has been completed for all sensors, the signal processor 224 then transmits a voltage supply signal to the second output terminal a(n).

Thereafter, frost formed on each cooling fin is sensed through an associated one of the plural sensors while executing the above-described operations 302 to 304.

When the frost sensing operation has been completely executed through the plural sensor, a voltage is supplied to the second output terminal a(n), which is not connected to any sensor (305). The signal processor 224 then receives a signal from the second input terminal b(n), which is not connected to any sensor (306).

Subsequently, the signal processor 224 subtracts the output signal of the NC second input terminal b(n) from the frost sensing signal received from each of the first input terminal b(1), b(2), b(n−1), and b(n), and transmits the resultant signal to the controller 180 (307).

The controller 180 then determines the amount of frost formed on the cooling fin of each evaporator, using the received signal (308). Based on the result of the determination, the controller 180 controls a defrosting operation.

Thus, it may be possible to remove offset noise generated at the oscillator 222 and multiplexer 221 by subtracting the output signal of the second input terminal b(n) from the signal output from each of the first input terminal b(1), b(2), b(n−1), and b(n).

That is, the detector 220 may obtain only the voltage signal corresponding to a capacitance varied due to the frost formed on the cooling fin of the evaporator in accordance with removal of noise signals.

FIGS. 10A-10C depict graphs of frost sensing signals generated in a refrigerator in accordance with an exemplary embodiment.

In detail, FIGS. 10A-10C depict graphs of frost sensing signals representing results of frost sensing experiments carried out for about 16 hours using 6 sensors. In the experiments, low-pass filtering was executed for signals obtained after signal subtraction.

In FIG. 10A, the graphs S(1) to S(6) represent frost sensing signals from sensors, which are applied to the first input terminals of the multiplexer, whereas the graph S(7) represents a signal applied to the second input terminal, which is not connected to any sensor.

Referring to FIG. 10A, it may be seen that a signal containing a common noise component and noise from the oscillator is input to each of 7 input terminals.

In FIG. 10B, each of the graphs S(1) to S(6) represents a signal obtained by subtracting the signal represented by the graph S(7) from each of the frost sensing signals depicted in FIG. 10A.

Referring to FIG. 10B, it can be seen that although common noise is removed from each frost sensing signal depicted in FIG. 10A in accordance with subtraction of the signal represented by the graph S(7), noise of about 10 mV from the oscillator is still output.

In FIG. 10C, each of the graphs S(1) to S(6) represents a signal obtained after filtering an associated one of the signals depicted by the graphs S(1) to S(6) of FIG. 10B through a low-pass filter.

Referring to FIG. 10C, it may be seen that signals, which do not pass through the filter for low-pass filtering to remove noise caused by oscillation of the oscillator exhibit a standard deviation of about 1.9 mV, whereas signals passing through the filter exhibit a standard deviation of about 0.7 mV. From this, it may be seen that noise reduction of about 61% is obtained, as compared to signals not passing through the filter.

Thus, it may be possible to easily and accurately determine noise contained in a signal received from the frost sensor by determining, as noise, the signal received from the input terminal, to which the frost sensor is not connected, and subtracting the noise from the signal received from each input terminal, to which the frost sensor is connected.

As a result, it may be possible to accurately determine whether or not frost has been formed on an evaporator, and to accurately detect the amount of frost formed.

Accordingly, it may be possible to more accurately determine whether or not frost has been formed on the refrigerant tube and cooling fins of the evaporator, and to accurately detect the amount of frost formed. Also, it may be possible to accurately determine the point in time when a defrosting operation should be begun, and the point in time when the defrosting operation should be ended.

Thus, it may be possible to drive and stop the heater for the defrosting operation at appropriate points in time as the amount of frost formed on the evaporator and the defrosting operation completion time are accurately determined, and thus to optimize the defrosting operation. As a result, the heat exchange performance of the evaporator may be enhanced. Also, consumption of energy for the defrosting operation may be reduced. Thus, an enhancement in energy efficiency may be achieved.

Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents. 

1. A cooling apparatus comprising: a frost sensor to sense frost; a multiplexer having a first input terminal, to which the frost sensor is connected, and a second input terminal as a non-connected input terminal; a signal processor to subtract a signal input through the second input terminal from a signal input through the first input terminal, and to output a signal obtained by the subtraction; and a controller to detect an amount of frost sensed by the frost sensor, based on the output signal from the signal processor.
 2. The cooling apparatus according to claim 1, wherein a peripheral noise signal is input to the second input terminal.
 3. The cooling apparatus according to claim 1, wherein the signal processor removes a noise signal by subtracting the signal input through the second input terminal from a frost sensing signal as the signal input through the first input terminal.
 4. The cooling apparatus according to claim 1, wherein: the controller controls a defrosting operation based on the detected frost amount; and the cooling apparatus further comprises a heater to operate in accordance with a command from the controller, so as to execute the defrosting operation.
 5. The cooling apparatus according to claim 1, further comprising: a filter to allow a low-frequency signal component of a frost sensing signal generated by the frost sensor to pass through the filter.
 6. The cooling apparatus according to claim 1, wherein the signal processor allows a low-frequency signal component of a frost sensing signal generated by the frost sensor to pass through the signal processor.
 7. The cooling apparatus according to claim 1, wherein the signal processor converts an analog signal as a frost sensing signal generated by the frost sensor into a digital signal.
 8. The cooling apparatus according to claim 1, wherein the signal processor amplifies a frost sensing signal generated by the frost sensor to a predetermined level.
 9. The cooling apparatus according to claim 1, wherein the frost sensor is installed on at least one of an evaporator for a refrigerating compartment, an evaporator for a freezing compartment, and an evaporator for an ice making compartment.
 10. The cooling apparatus according to claim 9, wherein the frost sensor senses a capacitance established between cooling fins provided at the at least one evaporator.
 11. The cooling apparatus according to claim 1, further comprising: an oscillator to supply a voltage to the frost sensor.
 12. The cooling apparatus according to claim 11, wherein the multiplexer further has a first output terminal, to which the frost sensor is connected, and a second output terminal as a non-connected output terminal, and supplies the voltage to a selected one of the first and second output terminals.
 13. The cooling apparatus according to claim 1, wherein: the frost sensor comprises a plurality of sensors; and the sensors are connected to the first output terminal and first input terminal of the multiplexer, and the sensors sequentially receive a voltage, and transmit a frost sensing signal to the first input terminal.
 14. A frost detecting method in a cooling apparatus, comprising: supplying a voltage to a frost sensor through a first output terminal of a multiplexer; sensing frost by the frost sensor; receiving a frost sensing signal generated by the frost sensor through a first input terminal of the multiplexer; receiving a signal from a second input terminal of the multiplexer; subtracting the signal of the second input terminal from the frost sensing signal; and detecting an amount of frost, based on a signal obtained by the subtraction.
 15. The frost detecting method according to claim 14, wherein the subtraction of the signal of the second input terminal from the frost sensing signal is executed to remove a peripheral noise signal from the frost sensing signal.
 16. The frost detecting method according to claim 14, further comprising: determining a point in time when a defrosting operation should be begun, based on the detected frost amount; driving a heater at the determined time point when the defrosting operation should be begun; determining, during the defrosting operation, a point in time when the defrosting operation should be ended; and stopping driving of the heater at the determined time point when the defrosting operation should be ended.
 17. The frost detecting method according to claim 14, further comprising: passing a low-frequency component of the frost sensing signal generated by the frost sensor.
 18. The frost detecting method according to claim 14, further comprising: converting an analog signal as the frost sensing signal generated by the frost sensor into a digital signal.
 19. The frost detecting method according to claim 14, further comprising: amplifying the frost sensing signal generated by the frost sensor to a predetermined level.
 20. The frost detecting method according to claim 14, wherein the sensing of frost by the frost sensor comprises sensing a capacitance established between cooling fins provided on at least one evaporator.
 21. The frost detecting method according to claim 14, further comprising: supplying a voltage through the second output terminal of the multiplexer.
 22. The frost detecting method according to claim 14, wherein the second output terminal and the second input terminal are non-connected terminals.
 23. The frost detecting method according to claim 14, wherein: the frost sensor comprises a plurality of sensors each connected to the first output terminal and first input terminal of the multiplexer; and the supply of the voltage to the frost sensor comprises sequentially supplying the voltage to the sensors.
 24. The frost detecting method according to claim 23, wherein the reception of the frost sensing signal through the first input terminal of the multiplexer comprises sequentially receiving frost sensing signals from the sensors through the first input terminal. 